In ITU-T recommendation G.993.2 (VDSL2) there is no low power mode defined. This means that independent of whether there is traffic or not the VDSL2 modems run at full power. Power is wasted because it is used to transmit idle data. A modem will run at full power even if the user is not using the modem. This way of operation is not power efficient and implies that the operators as well as the CPE (Customer Premises Equipment) user will have to waste a lot of power just transmitting and receiving idle data.
For the previous DSL (Digital Subscriber Line) standard ADSL2/ADSL2+, a low power mode was defined. However, a problem with such a low power mode is that when a line exits low power mode, crosstalk from that line into neighboring lines increases suddenly, and hence these lines experience a sudden noise level increase which may cause service disruption. In systems such as VDSL2 which use higher frequencies, that problem gets even worse because of the increased crosstalk at high frequencies.
Further, low power mode was implemented as a reduction of the transceiver transmit power. In systems such as VDSL2, the transceiver transmit power is only a small part of the total power and so the power savings of the previous low power concept will be rather small.
For these reasons, a low power mode for VDSL2 has not been defined. A problem with VDSL2 is thus that when the line is idle, power is wasted.